How do you get bullies to f off?

Today at lunch in high school I was helping my friend learn to play the xylophone. We might have been a little loud or annoying but we sit outside so I didn't think it was a big problem. The freshmen/sophomores(I don't know which) that were sitting at a nearby table started to tell us to stop. We said it was for a school assignment because we had to build instruments for physics. Then some guys started throwing food at me because I was the one that was playing the instrument. I was really offended by it but didn't respond to their immaturity. After lunch I reported this incident to the assistant principals. They said that they would come tomorrow and to if they were still doing it. I don't want these guys to have a bad disciplinary record. Instead I just want them to know that they shouldn't be messing with me and that what they were doing is unacceptable. How should I act tomorrow in order to get them to f off? My friend says he wants to let them get further with their harrassing tomorrow so that he can say that he was provoked when he gets in a fight with them. But I don't want any physical violence. I want something powerful psychologically. Sorry for the long paragraph.